Polyurethane foams and methods for producing them are generally selected based upon the contemplated end use. Polyurethane foams produced from the reaction of polyols and toluene diisocyanate (TDI) are generally soft and flexible and they have thus been used when flexibility is required. In the past, greater than 80% of the toluene diisocyanate produced has been used to produce flexible foams. Polyurethane foams produced from the reaction of polyols and diphenylmethane diisocyanate are generally rigid and they have been used when strength and support have been required. In the past, 75% of the diphenylmethane diisocyanate produced has been used to produce rigid foams.
To produce a foam during the reaction of the polyol and the isocyanate, a foaming or blowing agent must be included in the reaction mixture. Fluorocarbon compounds, such as trichlorofluoromethane, have been used because they expand easily when heated and they do not react with the polyol and isocyanate. Fluorocarbon compounds continue to be used in the production of some rigid foams; however, methylene chloride has displaced most of the fluorocarbon compounds in the production of flexible foams. Water is also used as a foaming agent. Water reacts with the isocyanate to form an unstable acid which decomposes into carbon dioxide that creates the desired foaming. However, the reaction of the water and isocyanate has an undesired affect upon the reaction of the isocyanate and polyols such that the polyurethane produced is more rigid, or harder, than it would be if the water were not present. This undesired hardening of the foam has limited the use of water as the foaming agent in the production of flexible polyurethane foams.
In Japanese patent application 59-226034, published Dec. 19, 1984, a method for manufacturing a foamed urethane molded article is described. A urethane foam is produced from the reaction of a polyol and an isocyanate compound using both a fluorocarbon compound and a small amount of water as the foaming agents. Both toluene diisocyanate (TDI) and p,p'-diphenylmethane diisocyanate (MDI) were used as the isocyanate compound. A phthalic acid plasticizer, such as the specifically discussed di-2-ethylhexyl phthalate (DOP), butyl benzyl phthalate (BBP), and dibutyl phthalate (DBP), was added to the reaction to reduce the lower mold temperature required for molding the desired articles. This Japanese application teaches the production of rigid foams, as shown by the sphere penetration test; and the plasticizers are added to reduce the required mold temperature.